How to detect multiple playing cards of the same class with a neural network?
Although it was not crystal clear, we'll assume that by, "Multiple cards of the same class in one picture," is meant that multiple cards of identical suit and rank will be grouped together in the same example image but each card in the image will be selected from a unique deck.

That arrangement would only be fruitful if the objective of training was to classify, flag, or otherwise analyze the same kind of groupings after training. Otherwise, it would likely be most productive and efficient to first devise a way to divide up the images by deck so that the focus of learning is detection of the three dimensions or perhaps just the first two, depending on the intended use of the trained network.


Rank
Suit
Style